The invention relates to optical devices known as collimators.
A collimator includes a lens positioned in a output beam that emanates from a single mode optical fiber. The lens transforms the beam into an approximately parallel optical beam over an extended distance. Minimization of back-reflection from the fiber end necessitates an angle of approximately 8 degrees on the fiber output surface. This angled fiber-end, in turn, produces a radial offset of the parallel optical beam from the collimator axis. Centration errors in lenses produce angular offsets between the parallel optical beam and the collimator axis. Both of these offsets can prevent the collimated optical beam from reaching an intended target.
Fiber-optic networks use arrangements of collimators with micromachined mirrors to provide optical interconnect switching between optical fibers. These optical networks require that the collimators point input light beams towards the mirrors with great precision. More particularly, each of these collimators has a one to one direct correspondence to the mirror in front of it and needs to aim its beam directly towards the center of the corresponding mirror. As switches increase in size, the distance between the collimator and the corresponding mirror increases also, and the pointing becomes more of a challenge.
To achieve accurate pointing, collimators provide optical beams with small radial offset over various distances to the micromachined mirrors. In addition, the centration of the lens focus and the external cylindrical axis of the lens body must be better than 5 micron, a figure which is extremely difficult to achieve in the fabrication of lenses.
In one aspect of the invention, collimating an optical beam includes: providing a collimator body having a ferrule coupled to a concentric bore which is coupled to a lens holder for supporting a lens, the concentric bore being centered within the body around a first axis, the ferrule having an angled end fiber centered therein and being positioned within the body about a second axis that is inclined relative to the first axis, the axes forming a plane therebetween; and adjusting the position of the ferrule to position an optical beam exiting the angled end fiber within the plane along a path that is parallel to the first axis within the plane.
Embodiments of the invention may include one or more of the following features.
Collimating an optical beam can further include rotating the lens holder about the first axis to set an optical center of the lens in the plane, again adjusting the position of the ferrule and moving the lens holder in a direction parallel to the first axis to position the optical center at a desired distance from the angled end fiber.
Among the advantages of the present invention are the following. The collimating scheme of the invention produces a degree of pointing accuracy that is required by demanding applications like fiber-optic switching.
Other features and advantages of the invention will be apparent from the following detailed description and from the claims.